This invention relates to a hydrogenation process for selective non-destructive hydrogenation of alkylstyrene to produce alkylbenzene.
The major process employed for phenol manufacture involves hydroperoxidation of cumene (isopropyl benzene), followed by acid cleavage of the resulting hydroperoxide to produce phenol and acetone. A by-product of the hydroperoxidation reaction is .alpha.,.alpha.-dimethylbenzyl alcohol which, in turn can lose a mole of water to form .alpha.-methylstyrene. In order to obtain improved efficiency in the phenol production process from cumene, considerable effort has been made to convert the .alpha.-methylstyrene by-product to cumene by hydrogenation and recycling to the process. Also, in the manufacture of other alkylphenols via hydrocarbon hydroperoxidation, as for example, cresols from mixed cymenes, analogous chemical reactions take place. In this process, hydrogenation of the dimethylstyrene produces cymene.
In order to achieve economical hydrogenation of the alkylstyrene derivatives, it is desirable that the reaction occur under moderate conditions, in a manner that avoids excessive consumption of hydrogen, which can utilize relatively impure styrene feed streams and which can utilize impure hydrogen streams and especially those containing carbon monoxide. Also, it is important that the catalyst system be one which does not require expensive regeneration procedures and be one which has a relatively long catalyst life. Numerous catalyst systems have appeared in the art as the expensive platinums or palladium catalysts, such as disclosed in U.S. Pat. No. 3,127,452 and U.S. Pat. No. 3,436,429 which claim to eliminate the hydrogenation of the aromatic ring while selectively hydrogenating the alkenyl substituent on the aromatic ring. However, in practice these catalysts have been only partially successful in eliminating aromatic ring hydrogenation. Furthermore, a significant drawback relates to the fact that when attempting to use low grade hydrogen-containing streams such as those available from gasification or partial gasification of coal or oil, or with waste gases from commercial operations that contain appreciable concentrations of carbon monoxide, serious degradation and poisoning of the catalyst occurs.